Step 8: Wait 30 Minutes

Step 9: Still Frozen?

Step 10: Did You Know?

It’s all about stopping heat. A good insulator keeps heat from moving. For example, to keep something cold, an insulator stops heat from entering. To keep something hot, an insulator stops heat from leaving. And air is one of the best insulators around. Think bubble packaging. All that trapped air stops heat from passing through. Foam, fleece, and even crumpled paper trap air, too. Hey, how about a winter coat made out of crumpled paper!

Step 11: Try This Next!

Build an even better lunchbox. Use your materials differently to trap more air. Or use different kinds of materials. See if you can get less melting in 30 minutes.

Go for longer. Build a lunchbox that can keep something frozen for an hour. It helps to pre-cool the insulation and to keep the lunchbox away from serious heat.